1. Technical Field
The present invention relates to a technology for performing congestion control with a packet relay device.
2. Related Art
As a relay device for performing relay of packets or frames on a network, for example, routers, switches and the like are known. For this kind of relay device, when there is a communication request that greatly exceeds the allowed capacity, there are cases when communication becomes stagnated in the relay device interior. This kind of phenomenon is typically called “congestion.” Regardless of the network scale, this is a phenomenon that can occur with a LAN, WAN, the internet or the like.
As technology for suppressing this kind of congestion, for example, there is the technology noted in JP-A-1998-0173661. With this technology, a judgment is made of whether or not the value of a FIFO length counter for monitoring the number of packets buffered in the overall FIFO memory has exceeded a specified threshold value. Then, when the value of this FIFO length counter does exceed the threshold value, control is performed to uniformly reduce the threshold value for monitoring the number of packets prepared individually for each connection. With this kind of control, notification to the effect that congestion has occurred is given to sending source terminals connected to connections with a larger number of buffered packets than the reduced threshold value. When the sending source terminal receives this notification, it can reduce the packet sending volume. Because of this, the packets received from that connection are decreased from FIFO memory, and it is possible to suppress the occurrence of congestion.
However, with the technology disclosed in JP-A-1998-0173661, because the threshold values prepared for each connection are reduced uniformly, notification to the effect that congestion has occurred is given to all the sending source terminals connected to connections with a higher number of buffered packets than the reduced threshold value. When this happens, because the packet sending volume is simultaneously reduced by all of those sending source terminals, there are cases when there is a sudden decrease in the overall network throughput. This kind of problem is not restricted to packets but rather is a problem that can occur in common with devices that perform relay of data flowing on a communication line such as a network or the like.
Consequently, there is a need for a congestion control technology capable of suppressing a decrease in overall network throughput.